This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to Appln. No. 199 58 646.2 filed in Germany on Dec. 6, 1999; the entire content of which is hereby incorporated by reference.
The invention relates to a hybrid circuit breaker.
The document EP 0 847 586 B1 discloses a hybrid circuit breaker which can be used in an electrical high-voltage network. This hybrid circuit breaker has two series-connected arcing chambers, a first of which is filled with SF6 gas as an arc extinguishing and insulating medium, and a second of which is in the form of a vacuum switching chamber. The second arcing chamber is surrounded by SF6 gas on the outside. The main contacts in the two arcing chambers are operated simultaneously via a lever transmission from a common drive. Both arcing chambers have a power current path, in which the consumable main contacts are located, and a rated current path in parallel with it, with this rated current path having only a single interruption point. On disconnection, the rated current path is always interrupted first, after which the current to be disconnected commutates onto the power current path. The power current path then continues to carry the current until it is definitively disconnected.
In this hybrid circuit breaker, the arc which always occurs in the vacuum switching chamber during disconnection burns for approximately the same time period as in the gas-filled first arcing chamber, which means that the main contacts in the vacuum switching chamber are subjected to a comparatively high and long-lasting current load and, linked to this, a high wear rate, which means that maintenance work has to be carried out comparatively frequently, as a result of which the availability of the hybrid circuit breaker is limited. This hybrid circuit breaker requires a comparatively large amount of drive energy since, depending on the switching principle used in the gas-filled first arcing chamber, the drive has to produce all or part of the high gas pressure required for intensively blowing out the arc. Such a drive, which is designed to be particularly powerful, is comparatively expensive.
After the arc has been extinguished, the returning voltage that occurs across this hybrid circuit breaker is distributed between the two arcing chambers in a corresponding manner to the intrinsic capacitances of these arcing chambers. This means that the second arcing chamber, which is in the form of a vacuum switching chamber, has the majority of the returning voltage applied to it, so that this second arcing chamber strikes while the returning voltage is rising. This striking can occur a number of times during a disconnection process. The striking can initiate undesirable oscillation processes in the high-voltage network, linked to undesirable voltage rises. Furthermore, the striking process additionally stresses the consumable contacts in the vacuum switching chamber, so that their life is shortened.
Laid-open specification DE 3 131 271 A1 discloses a hybrid circuit breaker, in which the voltage distribution across the two switching chambers is attainable by means of a capacitance which is connected in parallel with the first switching chamber, which is insulated and blown by a gas, and by means of a nonlinear resistance connected in parallel with the second switching chamber, which is in the form of a vacuum switching chamber. During the rise of the returning voltage immediately after the interruption of the arc, these two components ensure that the majority of this returning voltage is first of all applied to the vacuum switching chamber, which withstands it. Subsequently, the first switching chamber then takes over the majority of the applied voltage. These two components for controlling the voltage distribution require a comparatively large volume in the interior of the switch housing of the hybrid circuit breaker, so that the circuit breaker requires a comparatively large, and therefore also expensive, switch housing.
The invention achieves the object of providing a hybrid circuit breaker which can be produced economically and which has a high availability.
In this hybrid circuit breaker the first, steep rise in the returning voltage is borne essentially by the second arcing chamber, which is in the form of a vacuum switching chamber. Accordingly, the dielectric recovery of the extinguishing path in the first arcing chamber may take place comparatively slowly, which means that the blowing in the first arcing chamber may be considerably less intensive than in conventional circuit breakers. Considerably less energy thus needs to be consumed to provide the pressurized gas required for blowing out the arc.
The advantages achieved by the invention are that the hybrid circuit breaker can be equipped with a considerably weaker and thus more economic drive for the same power switching capacity. Furthermore, the pressures which occur in the first arcing chamber in this hybrid circuit breaker are considerably lower than in conventional circuit breakers, so that the insulating tube and the other parts that are subjected to pressure can be designed for reduced loads as well, thus making it possible to design the hybrid circuit breaker to be more economic. Furthermore, it is advantageous that the flow rate of the gas which cools the arc in the first arcing chamber may be in the subsonic range since the blowing required in this case is considerably less intensive and, in consequence, the amount of pressurized gas that needs to be provided for blowing can be kept comparatively small. A further advantage is that the consumable contacts in the second arcing chamber which, in this case, is in the form of a vacuum switching chamber have a longer life owing to the shorter duration of the current load during disconnection and owing to the avoidance of the repeated striking process while the returning voltage is rising, and this results in advantageously improved operational availability of the hybrid circuit breaker.
The hybrid circuit breaker is provided with at least two series-connected arcing chambers which are operated by a common drive or by separate drives and are filled with different arc extinguishing media, wherein the arc extinguishing and insulating medium in the first arcing chamber surrounds the second arcing chamber in an insulating manner. Means are provided which ensure a technically sensible voltage distribution between the two arcing chambers during the disconnection process. Furthermore, means are provided which ensure that the movement of the first arcing chamber leads the movement of the second arcing chamber during the disconnection process. During the connection process, the second arcing chamber always closes before the first arcing chamber. A gas or a gas mixture is used as the arc extinguishing and insulating medium in the first arcing chamber. At least one vacuum switching chamber is provided as the second arcing chamber. However, other switching principles may also be used for the second arcing chamber.